The prior art is generally cognizant of metal frame members used for framing doors, windows, and the like. Commonly such frames are made by extruding aluminum or other selected metals. Such frames are strong, dimensionally accurate, and resist the effects of water and weather. However, because metal is a good heat conductor, they present difficulties when outside temperatures differ from those within the building equipped with such a frame. In the winter, the frames are cold, and water condensation and frost commonly form on their interior surfaces, leading both to water damage and to increased cost of heating. When exterior temperatures are warm in comparison with the temperatures inside the building, heat transferred through the frames into the building increases the cost of air conditioning and the like.
The prior art is cognizant of combining wood framing members with metal frames for aesthetic purposes. See Price, U.S. Pat. No. 3,042,160. The frame arrangement shown in Price provides for a partial covering of a prefabricated metal frame with wood trim pieces. However, the metal frame in Price has an uninterrupted metal heat flow path between substantial exposed exterior and interior parts. Metal is also visible from inside the window or other opening equipped with the Price frame.
The prior art is also cognizant of the use of structural heat transfer barriers incorporated in the metallic parts of metal framing members. See Nilson, U.S. Pat. No. 3,204,324. Such structural heat transfer barriers serve to thermally insulate inner parts of the frame from outer parts so that there is no continuous, metallic path by which heat can flow between the interior and exterior parts of the frame. Such framing members exhibit greatly improved heat flow characteristics over comparable framing members having no structural heat transfer barriers. However, with fuel costs escalating rapidly, even better systems are required to reduce heat transfer through wall opening frame members, particularly when temperature differences are extreme between the exterior and interior of the building in which such a framing member is mounted. In addition, the metal framing of Nilson may be esthetically objectionable in many building environments where wood framing members have traditionally been employed, even though metal members may be structurally superior.
Accordingly a need exists for a wall opening frame member which conbines the structural strength, dimensional accuracy and lonevity of metal with the insulating and esthetic qualities of wood.